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From "Richard Huddleston (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-6036) If you wrap a SELECT * view around a table, all of the columns are read from the base row even when you SELECT only a subset of the view columns.
Date Fri, 13 Dec 2013 14:45:16 GMT

    [ https://issues.apache.org/jira/browse/DERBY-6036?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13847533#comment-13847533
] 

Richard Huddleston commented on DERBY-6036:
-------------------------------------------

unfortunately we cannot use the foreign views / ForeignTableVTI as we are writing our own
adapter to greenplum. 

we use derby as a front end to greenplum. we use derby to parse the sql and then we submit
the query to the greenplum master and instead of getting a result in the jdbc connection,
 we do an ETL write to an external servlet which is running in derby.  ETLs in greenplum are
VERY fast and prevent the bandwidth crunch on the master greenplum node.  In the ETL, EACH
of our greenplum slaves reaches out individually to the derby instance to post back result
sets, and does NOT use any resources on the master. Data gets pushed back to our derby instance
at greater than 1 gbit/sec, and our resultset merges the multiple http posts back into a single
result.  People love our derby frontend to greenplum, and now are thinking about other systems
we should expose through derby. but our system is not as fast as it could be.


> If you wrap a SELECT * view around a table, all of the columns are read from the base
row even when you SELECT only a subset of the view columns.
> -------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: DERBY-6036
>                 URL: https://issues.apache.org/jira/browse/DERBY-6036
>             Project: Derby
>          Issue Type: Bug
>          Components: SQL
>    Affects Versions: 10.10.1.1
>            Reporter: Rick Hillegas
>              Labels: derby_triage10_11
>         Attachments: derby-6036-01-aa-testForRestrictionPushing.diff, derby-6036.sql,
derbyAST.xml
>
>
> This also affects SELECTs from views wrapping RestrictedVTIs. Restrictions are pushed
into a restricted VTI if you wrap it in a view. However, projections are not. I will attach
a script showing this problem.



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